Method and apparatus for heat-treating granulated expansible materials



March 11, 1969 Filed April .5, 1965 A H. DENNERT METHOD AND APPARATUS FOR HEAT-TREATING INVENTOR 4 61/15 Dena. e 't March 11, 1969 DENNERT 3,432,155

METHOD AND APPARATUS FOR HEAT-TREATING GRANULATED EXPANSIBLE MATERIALS A Filed April 5. 1965 Sheet & of 4 DENNERT METHOD AND APPARATUS FOR HEAT-TREATING March 11, 1969 GRANULATED EXPANSIBLE MATERIALS sheet Filed April 5, 1965 March 11, 1969 H DENNERT 3,432,155

METHOD AND APPARATUS FOR HEAT-TREATING GRANULATED EXPANSIBLE MATERIALS Filed April 5, 1965 Sheet 4 of 4 United States Patent 28 Claims ABSTRACT OF THE DISCLOSURE In a method of expanding an expansible granular material, and an apparatus for performing the method, there exists a vertical reaction chamber having a burner chamber underneath, the two chambers being coaxial and having a central neck like opening connecting them. A plurality of gas burners mounted substantially radially inwardly in the outer perimeter of the burner chamber to provide a gas current which flows toward the vertical axis of the burner chamber where the gas currents combine and deflect upwardly through the neck like opening into and through the reaction chamber and out the upper end thereof. Granular material is intermittently charged into the reaction chamber, enters the ascending gas current, and reach a point in height where the buoyancy of the gas current no longer exceeds the gravitational force on the particle, and the particles separate from the as cending gas current and fall by gravity outside the gas current along the wall of the reaction chamber toward the necklike opening where they are again picked up and carried upwardly by the gas current. This circulatory movement of the granular material is continued, and intermittently the extended particles are removed. According to a further embodiment a vertical guide element can be placed coaxially within the burner chamber so as to project at least into the necklike opening.

The present invention relates to a method and an apparatus for heat-treating granulated expansible materials, especially for producing a material which is hereafter called expanded clay, although the invention is by no means limited to this particular expansible mineral and the treatment thereof.

In this method, the granulated material is subjected in a reaction chamber to the influence of a hot gas. This results at first in the formation of a thin plastic glasslike wall on the outer side of each grain which is followed by a development of gas within the grain, whereby the grain is expanded like a balloon. By this treatment, a small grain of a large specific mass is converted into a large, substantially spherical grain of a small specific mass. Because of its low bulk weight, expanded clay is of great importance as an aggregate producing lightweight structural elements, for example, of light concrete.

In the production of expanded clay it has so far been a very difficult problem to prevent the agglomeration or caking of the grains, the outer surfaces of which have become plastic. The best possible solution was at first the fluidized-bed or fluidization method, i.e. the operation with a fluidized layer which was carried out on a grate or freely on a gas current. The results which were attainable by these methods were, however, unsatisfactory since the accumulation of the grains within the fluidized layer was still so large that a caking of the grains could occur.

Considerable progress in this art was attained by the treatment of the granulated material in a continuous vertical circulating current which was produced by an ascending gas current in a reaction chamber. A formation of layers was then intentionally avoided and efforts were made to maintain the grains as separately from each other as possible so as to prevent them from caking together.

This method which is described, for example, in the French Patent No. 1,320,742 consists of feeding the grains into a hot ascending jetlike gas current which carries them upwardly in the reaction chamber. At a point near the top of the reaction chamber, the grains are then deflected so as to leave the hot gas current. The grains then drop by gravity back to the point of entry of the gas current into the reaction chamber where they are again picked up and taken along by the gas current in the upward direction. This circulation is continued until the entire charge of grains is completely expanded. This method has proved very successful and it also constitutes the basis of the present invention. However, it still possesses certain disadvantages which the present invention is intended to overcome.

For treating expansible clay in a hot gas current there have been numerous suggestions according to which the granulated material is to be fed directly into the hot flames. Such a method has, however, especially the disadvantage that it cannot avoid the effects of the considerable differences in temperature which occur within the cross-sectional area of the flames. Depending upon their particular location within the flames, the grains are therefore subjected to greatly varying temperatures. For expanding clay particles, it has therefore been found more advisable to arrange the burners in such a manner that the material will not come in direct contact with the flames themselves, but only with the burned-out flue gas. The burners are then mounted within a chamber adjacent to or underneath the reaction chamber and at such a distance therefrom that the flame will. be burned out before the hot gas comes in contact with the clay particles. This requires the hot gas current to be deflected from its original direction so as to flow into the reaction chamber in the axial direction of the latter.

Extensive experiments and tests have shown that the conditions which actually occur in the operation of such an apparatus lead to results which can hardly have been foreseen. In order to produce in front of the reaction chamber a gas current which is uniform at least to some degree, a tubular member which had an effect similar to a nozzle was inserted between the burner chamber and the reaction chamber. This was done on the assumption that the gas current might thus be given a substantially homogeneous flow behind the point of its deflection from the transverse burner chamber in the direction of the longitudinal axis of the reaction chamber. Actually, however, this does not occur. On the contrary, the flow is very unequal within different parts of its cross-section. At the upper edge of the mouth of the reaction chamber a lowpressure area is formed, while a pressure area exists at the opposite nozzle wall upon which the gas current impinges. The different parts of the gas current, as seen in a cross-section thereof, therefore have very different velocities. That is, however, very undesirable for the required treatment of the grains. There is, however, still another very serious disadvantage which occurs in the operation of such an apparatus. At the point where the gas current impinges upon the opposite nozzle wall a static high temperature area will be formed which has a temperature higher than that to which the grains may be exposed in the reaction chamber. If during the movement of the grains within the reaction chamber or while passing out of this chamber some of them might come in contact with the hot wall portion of the nozzle, they will cake tightly thereon and form a thick layer which not only constitutes lost material but also obstructs the free flow of the gas current. All efforts which were made to attain a uniform gas current by superimposed forced-flow currents and similar means proved unsuccessful. Although the uniformity of the gas current may be very slightly improved by considerably increasing the length of the tubular nozzle member, this results in a very uneconomical increase in height of the entire furnace structure, but does not eliminate the above-mentioned disadvantages, namely, the excessive heating of a part of the neck of the furnace.

It is an object of the present invention to solve all of these problems by providing the burner chamber in the form of an annular chamber which is equipped with a plurality of burners which are distributed along the periphery of this chamber. One very important advantage which is hereby attained is that the flames may be shortened very considerably. Since the fuel consumption of each individual burner of such a burner assembly only amounts to a fraction of the total consumption of fuel of the single burner of the apparatus as were previously used, only a relatively short flame will now be formed. Consequently, the size of the burner chamber transversely to the reaction chamber and thus also the space required for erecting the apparatus is considerably smaller. Furthermore, there is now no longer any possibility that extreme nonuniform temperature and velocity areas might form. Even if some differences between some parts of the gas current might occur at the point of its passage from the burner chamber into the reaction chamber, these differences compensate each other symmetrically. An unsymmetrical flow of the gas current therefore no longer occurs but the gas now passes out of the burner chamber in a substantially homogeneous flow.

It has already been mentioned above that the annular burner chamber with its large number of burners results in a considerable reduction in the length of the individual i flames. If the flames should still be too long in view of the permissible size of the apparatus, their length may be further reduced by providing each burner with an additional air nozzle which has an axis extending either transverse or opposite to the direction of the flame and is therefore adapted to blow an air current in the mentioned direction which forms the secondary air for the combustion and produces a strong turbulence of the fuel and air mixture so that an instantaneous combustion occurs.

Important advantages may be further attained according to the invention by providing at least the upper and lateral sides of the annular burner chamber with double walls so as to form a channel between these walls through which the air may be supplied to the burners and to the secondary-air outlet openings. By this double-wall construction it is possible to build the walls of the burner chamber of heat-resistant steel instead of requiring a heavy, complicated construction of refractory masonry or the like. These Walls will then be protected from overheating by being cooled by the air which is conducted between them.

This cooling air thus takes up the heat of the steel walls so that it is then passed to the flame in a preheated condition. Such preheating of the combustion air further increases the intensity of the combustion.

By building the walls of the burner chamber primarily of steel, this chamber becomes thermally very elastic since the thermally inert masses are very small in comparison to those of burner chambers of masonry.

The objects, features, and advantages of the present invention will become more clearly apparent from the following detailed description thereof which is to be read with reference to the accompanying drawings, in which:

FIGURE 1 shows a partial vertical section of a reaction chamber and a full line elevation of the annular burner chamber underneath the reaction chamber;

FIGURE 2 shows a vertical section of the lower part of the apparatus according to FIGURE 1;

FIGURE 3 shows a vertical section of a burner chamber according to a modification of the invention;

FlGURE 4 shows a vertical section of an apparatus similar to that as shown in FIGURE 2, but additionally provided with a guide element;

FIGURE 5 shows a vertical section of a guide element according to a modification of the invention; while FIGURE 6 shows a diagrammatic illustration of the circulating current of the granlated material in the reaction chamber and of the flow conditions within this chamber.

Referring first to FIGURES l to 3 of the drawings, the apparatus according to the invention comprises a reaction chamber, the particular shape and construction of which does not constitute a feature of the invention and which is illustrated as consisting, for example, of a cylindrical wall 1 of refractory material which is provided at its upper end with a line 1 and has a lower part 2 of a conically reduced shape which is connected to the burner chamber 4. The material to be treated is to be supplied to this reaction chamber through one or more inlet ports 3. The particular location of the inlet port or ports 3 on the wall 1 of the reaction chamber and the manner in which the material is supplied, whether by gravity or by means of a conveyor, for example, worm conveyor, are also not important insofar as the invention is concerned. The lower side of the burner chamber 4 is provided with an outlet channel 5 for the treated material which is closed during the treatment by a conical closing member 6 and is adapted to be lowered for the removal of the treated material.

The burner chamber 4 has a shape of a box ll of a circular or polygonal cross section and it is made of steel except its bottom which consists of a plate 8 of a refractory material. The outer peripheral wall of the burner chamber 4 carries a plurality of burners 9, as illustrated diagrammatically, which are peripherally spaced from each o.her and are preferably supplied with fuel by a pump through a common fuel supply line which is connected to the individual control valves it} of the burners. The fuel gases flow radially toward the inside of the burner chamber and are then deflected by the conical baffie surface 11 in the direction toward the axis of the reaction chamber 1, 2. The conical surfaces 11 and 12 form the inner wall of the box 7 which is provided with inlet ports 13 for the supply of compressed air. Box 7 further contains a wall 14 which is spaced from and has a shape similar to the inner wall 11, T12 so that a chamber or channel 29 is formed between the walls ll, 12, and 14. This chamber 25lcommunicates through bores or short tubes 15 with the chamber 16 in the box 7. The numeral 18 indicates an annular chamber which communicates through apertures 9 with the chamber 20. Burners 9 are surrounded by short tubes 21 which project slightly into the annular chamber 18. The compressed air is therefore supplied from the inlets 13 through chamber 16, tubes 15, chamber 20, apertures 19, annular chamber 18, and tubes 21 to the burners 9 where it serves as primary air. This air current has the additional purpose of intensively cooling the walls of box 7 which are exposed to high temperatures. This permits these walls to be made of steel. The heat which is taken up by the air current is thus returned into the circulation.

It has previously already been indicated that it is of considerable advantage to inject air into the burner chamber in a direction transverse or opposite to the direction of the flames. The nozzles which are employed for this purpose are designated by the numerals 22. The air which enters the burner chamber through these nozzles forms the secondary air for the combustion process and also produces a very strong turbulence of the fuel gas currents.

According to a modification of the invention, as illustrated in FIGURE 3, the lower end of the tapered bottom part 2 of the reaction chamber is provided with a guide surface which is preferably trough-shaped and extends in the direction toward the gas current for guiding the grains which are falling downwardly back into the gas current in a manner similar to a ski jump. These grains are therefore guided by this preferably trough-shaped guide surface so as to be returned with a certain velocity into the gas current. The falling speed of the grains is hereby not substantially retarded and their gravitational energy no longer needs to be dissipated but, on the contrary, it will be utilized for a very advantageous purpose. In this manner it is possible to reduce the velocity of the gas current and thereby to reduce the energy contained therein to such an extent that this velocity will be slightly higher than the falling speed and will suffice for carrying the grains in a vertically upward direction. This results in a considerable increase in the efficiency of the reaction chamber and in a saving in energy. Due to the reduction in the velocity of the gas current, the grains will also be protected and a wear thereon will be avoided. Furthermore, the height of the reaction chamber may now be considerably reduced and a deflecting plate on the upper end of the chamber may be omitted.

In order to prevent the downwardly returning grains from accumulating on the trough-shaped guide surface, the invention further provides a slot-shaped channel which extends substantially tangentially to the guide surface from the outside to the inside of the combustion chamber and serves for conducting a gas, especially air, at an increased velocity through this channel and along the trough-shaped guide surface so as to blow the grains out of the latter and thereby to increase their velocity so as to approximately equal to the velocity of the gas current. This also has the advantage that no eddy currents will be formed. The gas which is inserted through the slot-shaped channel may be either cold or preheated, for example, to the same temperature as that of the gas current in the center of the chamber. The added gas may also have the same velocity as this main gas current or it may be branched off from the latter.

An apparatus as above described is diagrammatically illustrated in FIGURE 3. The surface 12' is not obliquely inclined in the downward direction like the surface 12 in FIGURE 2, but it is curved upwardly. This guide surface may, however, also be straight and extend either upwardly or downwardly. The movement of the grains 23 is aided by air currents which are supplied through nozzle ducts 24.

It may be assumed that, due to the vertical circulating current, the upward movement of the grains depends solely upon the difference between the buoyancy of the gas current and the gravity of the grains. in other words, there is a definite culmination point where the gravity of the grains is equal to the buoyant force which is exerted upon the grains by the ascending gas current since the buoyant force of the gas current decreases in proportion to its ascent. This also applies to most of the grains, but not necessarily to all of them, especially not to those near the center of the gas current. A gas current passing into a chamber of a larger cross-sectional size will not remain a closed column but will more or less expand to a conical shape. The buoyant force which is exerted upon the grains is therefore the greatest within the center or core of the gas current where the grains are given a strong impulse.

By way of comparison it may be said that within the core of the gas current the grains will be shot rather than carried in the upward direction. Consequently, at least those grains which are located within the core of the current will be given anacceleration which exceeds the upwardly decreasing buoyant force and conveys the grains beyond the culmination point. These grains will then hit with a considerable impact upon the deflecting surface which has the result that not only the deflecting surface will be severely and quickly worn but that the grains will also be worn. These are very serious disadvantages of similar apparatus which were heretofore known and it is another object of the invention to eliminate or at least to reduce these disadvantages considerably.

A further object of the invention which is functionally connected herewith is the following:

The reaction chamber has a lower part of a conical shape for guiding the returning grains back to the entry of the gas current. It has already been mentioned that the descending branch of the circulating current of grains proceeds under the action of gravity. Just as the gas current contains core zones, the buoyancy of which considerably exceeds the gravity of the grains, it also has marginal zones the buoyancy of which has an intensity lower than the gravity acting upon the grains. The result will therefore occur that the grains which are picked up by the core of the current will be propelled upwardly too strongly and will therefore be expelled, while the grains which pass into the marginal zones will fall downwardly because of an insufficient lift and will not enter again the circulating current.

Two problems therefore arise, namely, that of avoiding the discharge of individual grains from the circulating current in the upward direction and that of avoiding the dropping of grains through the current.

It would be too lengthy to describe all of the experiments and tests which were carried out in order to solve these problems. In general, it was found that, when it was possible to avoid the discharge of grains in the upward direction, the grains always dropped to the bottom against the gas current. In the opposite case, when it was possible by an increased velocity of the gas to prevent the grains from dropping through, a discharge occurred in the upward direction since the culmination point was then elevated to a higher level, namely, up to the area near the flue at the top of the reaction chamber.

According to the invention, it was finally discovered that these problems may be solved by passing the gas into the reaction chamber in the form of a coreless annular or tubular current.

This general concept of the invention may be carried out in actual practice very advantageously in such a manner that, after the coreless tubular current has entered the reaction chamber, it is deflected toward the Wall of the reaction chamber in the form of a coreless conical tubular current.

The fundamentally new effect of the coreless tubular current is that the velocity peaks and thus the buoyancy peaks are avoided which would otherwise occur in the core of the current. The velocity is now' made considerably more uniform, the buoyant forces are therefore distributed as uniformly as possible throughout the entire annular cross section of the current, and individual grains are no longer shot out of the curent at the culmination point in the manner as it would occur if the current had a core.

The modification of the new method, i.e., the mentioned formation of a conical tubular current which is deflected toward the wall of the reaction chamber, differs from the above insofar as the grains do not reverse their direction of movement of their own accord at the culmination point of their circulation, but they will hit upon the wall and then slide downwardly along the same. Since the force component is not very considerable when the grains hit upon the wall at an acute angle, the undesirable wear on the grains will also not occur. The particular advantage of this modified method is the fact that the height of the reaction chamber may be reduced very considerably.

The elements of the apparatus which are essential for carrying out this modified method consist of an annular burner chamber and a guide element which is mounted centrally on the bottom of the reaction chamber and is adapted to convert the hot gas current as it enters the reaction chamber from the burner chamber into an annular current.

In order to divert the gas current which enters the burner chamber transversely to the reaction chamber so as to pass smoothly in the desired direction into the reaction chamber, the invention further provides that the mentioned guide element is provided with a concave guide surface.

Reference may already be made at this point to a preferred embodiment of the invention, the features of which will be later described in detail. It has previously been mentioned that the material which drops back downwardly at the outside of the tubular gas current is guided toward the center of the lower part of the reaction chamber by making the wall of this lower part of a conical shape. The invention now provides that the extension of the generatrix of this cone intersects with the concave guide surface of the guide element.

The shape and construction of the guide element depends upon the particular shape of Which the coreless tubular gas current is to be made. If the tubular current should have a cylindrical shape, the concave lower guide surface should merge into a vertical cylindrical surface. If, however, the tubular current should have a conical shape, the guide element should be made of a shape similar to a mushroom with a constricted central part and a conical upper part so that this upper part will deflect the gas in the direction toward the wall of the reaction chamber.

This guide element consists according to the invention of a highly refractory material, preferably an alloy, for example, of the type which is known under the trademark Sicromal (Si-Cr-Mo steel). Since the guide element is located within the hottest area of the apparatus, it is provided with means for cooling it internally, preferably by a circulation of air.

It has previously already been mentioned that the problem of treating the granulated material in the form of a continuously circulating current has two components, namely, that of preventing the loss of some of the grains by being discharged from the reaction chamber in the upward direction and that of preventing the loss of grains by dropping out of the circulation in the downward direction. Both components of this problem may be solved in the manner as has just been described by the provision of a guide element which is adapted to form a coreless tubular jetlike current. Another feature of the invention for still more securely preventing the loss of grains by dropping out of the reaction chamber consists in providing the lower part of the guide surface of the guide element with apertures through which air under pressure, for example, some of the cooling air which is employed for cooling the guide element from the inside, is blown into the gas current in such a direction that the material coming down from the wall of the reaction chamber and then hitting upon the guide element will be caught and stopped by this air current near the lower end of the guide elementpossibly in cooperation with suitable stop surfaces or bafiles-and will then be blown back by this air current into the main gas current which will then carry this material again in the upward direction.

This additional feature of the invention of providing a guide element in the annular burner chamber may be more clearly illustrated with reference to FIGURES 4 and 5, in which the burner chamber may otherwise be of the same type as described with reference to FIGURE 2.

Similarly as shown in FIGURE 2, the discharge aperture 33 in the bottom 8 of the burner chamber 4 according to FIGURE 4 may be closed by a conical closing member 6 which may be lowered when the expanding treatment of the granulated material has been completed so as to permit the finished material to be removed. According to this embodiment of the invention, however, the conical closing member is connected to a guide element 34 which is therefore moved together with the closing member 6. The guide element 34 may, however, also be mounted in a stationary position on the bottom 8 of the burner chamber 4 and the closing member 6 may form a separate element which may be moved upwardly and downwardly. However, in this event it would be necessary to make the annular discharge opening 33 quite large so as to permit the expanded material to fall therethrough.

By the provision of the guide element 34, the gas coming from the burner chamber will now be guided along two surfaces, namely along the surface 11 of the box 7 and the surface of the guide element 34. The gas will therefore no longer form a full beamlike current but a coreless tubular current which in this particular case will not flow upwardly in a vertical direction, but at a certain angle toward the inner surface 36 of the cylindrical wall 1 of the reaction chamber since the guide surface 35 merges into the conical upper part 37 of the guide element. The grains which pass into this tubular current will therefore be thrown against the inner wall 36 of the reaction chamber, but at such an acute angle that they will slide along this Wall without being damaged or worn by the impact.

The particular cross-sectional shape of the guide element 34, whether it is circular or polygonal, is of no importance for the invention. As seen in its longitudinal direction, it is, however, of particular advantage to make it of the mushroom shape, as illustrated in FIGURE 4.

The guide element 34 is divided by an inner wall 33 of a shape similar to that of the outer wall into the chambers 39 and 40 through which a current of compressed air is passed. Since it is assumed in FIGURE 4 that the guide element 34 should be movable together with the conical closure member 6, the air should be supplied to the chamber 39 by means of a flexible hose 41.

The air is supplied to the inside of the guide element 34 primarily for the purpose of cooling it. According to the additional feature of the invention, as briefly mentioned above, it has, however, also a functional purpose. Near its lower end, the guide element is provided with a series of nozzle like apertures 42, each of which has an axis extending upwardly at an oblique angle, that is, substantially vertically to the direction of flow of the fuel gas in this particular area, so that a series of jetlike air currents are directed at an angle into the gas current. Although normally the granulated material should not fall through the most constricted part 43 between the edge 44 and the guide surface 35, this cannot be entirely avoided. If the material after dropping through this constricted part 43 slides further downwardly and passes into the area near the nozzles 42, it will be caught by a strong jet of air which will force it into the burner channel 45 where it will again be picked up and taken along by the gas current. Thus, there will be no accumulation of grains on the bottom of the burner chamber.

According to another feature of the invention it is possible to guide the granulated material still more accurately. Whereas in other embodiments of the invention the wall 12 of the box 7 may simply form a straight 6X- tension of the wall 32 of the burner chamber, this wall 12 may be inclined in such a direction that those of the grains which after sliding or rolling downwardly along the same might pass through the annular gas current will hit upon the guide surface 35 and will thereby be forced to move along the same toward the nozzles 42 Where they will be picked up by the air which is blown through these nozzles and will thereby be forced back into the gas channel 45 of the burner chamber. This effect may be further improved according to the invention by providing directly underneath the nozzles 42 an annular baffle or stop surface 46, preferably of refractory material, which catches any grains which might have dropped this far so that they will then be blown along this surface 47 back into the gas current by the air passing through the nozzles 42.

The further modification of the invention, as illustrated in FIGURE 5, is similar in principle to the apparatus as shown in FIGURE 4. However, the guide element 34a is in this case not of a shape similar to a mushroom but of a shape similar to that of a spindle of a spinning machine insofar as the curved lower guide surface 21 merges into a substantially smooth cylindrical surface 48. This results in a coreless tubular gas current of a substantially cylindrical shape in which the granulated material will be taken along upwardly in a substantially vertical direction. Whether a guide element 34 of the shape as shown in FIGURE 4 or a guide element 34a of a shape as shown in FIGURE 5 may be more suitable in actual practice must be determined by tests since this depends largely upon the nature of the particular granulated materials which are to be treated.

In connection with the annular burner chamber, there is still another problem which is to be solved by means. of the present invention.

In order to withdraw the grains from the ascending gas current and then to deflect them downwardly, a deflecting plate may be provided in the upper part of the reaction chamber or the head of the chamber may be designed so as to carry out the function of a deflecting plate. In the experiments and tests leading to the present invention it has been found that the deflection of the grains by means of a deflecting surface is unsatisfactory and may impair not only the deflecting surface but also the grains. The deflecting surface is not only exposed to very high temperatures, but it will also be eroded by the continuous impacts of the grains. It will therefore have to be repaired or completely exchanged after the apparatus has been in operation for only a short time. On the other hand, the use of a deflecting surface has the result that, due to the impact of the grains upon this surface, the grains will be considerably worn and some of them may even be seriously damaged.

According to another feature of the invention it is possible to overcome these disadvantages by making the reaction chamber of such a height that its upper wall will be located above the culmination point of the circulating current of grains. The course of the vertical circulating current of grains within the reaction chamber is determined by the buoyant force at the entry point of the gas current, by the decrease of this force in the direction of the gas current, and by the size .and the specific substance of the grains. When employing a deflecting plate, the upward movement of the grains will be interrupted, their velocity will be destroyed, and they will be deflected from their vertical course toward the side wall of the reaction chamber. If the current is left alone and not interrupted by an obstruction, it will reach a point in which the buoyant force of the gas acting upon the grains no longer exceeds their gravity. The ascending movement of the grains is then terminated at a culmination point similar to the jet of water of a fountain. Since the current is not free of turbulence, the grains will then change their direction, leave the further ascending gas current, and may drop freely downwardly under the action of their gravity. -If according to the invention the upper wall of the reaction chamber is located at such a high level that it lies above this culmination point of the circulating current of grains, the latter areprevented from hitting against this upper wall. No erosion or wear can then occur. If desired, a deflecting surface may, however, still be provided on the top wall of the reaction chamber in front of the gas outlet in orderto prevent very light grains from being carried away. Such a deflecting plate has, however, no longer the purpose of deflecting the grain current and it will therefore not be damaged. It is quite obvious that it is not possible to state any general rules for the height of the reaction chamber since it depends upon a series of factors, for example, the type of material to be treated, the size of the grains, the temperature, the velocity of the gas current, the amount of gas, etc. These influencing factors may, however, be predetermined for any particular material and for attaining a particular product, so that on the basis of these values it is easily possible either to calculate the proper height of the reaction chamber or to determine the same by tests. In view of these facts, the apparatus according to FIGURE 6 should be regarded only as a diagrammatic illustration without limitation as to the dimensions and particular locations of its individual parts.

The circulating current of grains in the reaction chamher 1 is indicated in FIGURE 6 by the dotted lines 50. Regardless of the dimensions of the reaction chamber 1, it is in every case of importance insofar as the invention is concerned that the culmination point 51 of the circulating grain current 50 is spaced at a certain distance H from the top wall 52 of the reaction chamber 1 so that the grains will never hit against this top wall. If a deflecting plate 53 is to be provided in front of the gas outlet or flue 6 in order to prevent very small and light grains from being carried out of the reaction chamber and from thus being lost, this deflecting plate should also be mounted at a height H above the culmination point 51.

Although my invention has been illustrated and described with reference to the preferred embodiments there of, I wish to have it understood that it is in no way limited to the details of such embodiments but is capable of numerous modifications within the scope of the appended claims.

Having thus fully disclosed my invention, what I claim is:

1. A method of expanding an expansible granular ma terial in a hot gas current in a vertical reaction chamber having a burner chamber underneath and substantially coaxial thereto and communicating therewith through a central necklike opening comprising the steps of injecting a plurality of gas currents of substantially equal velocity and size in substantially radial directions from the outside perimeter toward the vertical axis of said burner chamber, and then combining said gas currents and deflecting same as one substantially symmetrical beamlike gas current upwardly into and through said reaction chamber and then out of the upper end thereof; intermittently charging said reaction chamber with a predetermined amount of said granular material in the form of separate particles so as to pass said particles from above into the ascending gas current; maintaining a repeated circulating movement of said particles in said reaction chamber in which during the ascending part of said movement said particles are carried upwardly by said gas current to a point near the upper end of said chamber, whereupon said particles are caused to separate from the further ascending gas current and to fall by gravity outside of said gas current along the wall of said reaction chamber toward said necklike opening where said particles are again picked up and carried upwardly by said gas current; and then intermittently removing the expanded particles from said reaction chamber.

2. A method of expanding an expansible granular material in a hot gas current in a vertical reaction chamber having a burner chamber underneath and substantially coaxial thereto and communicating therewith through a central necklike opening, and further having a vertical guide element within said burner chamber coaxially with said reaction chamber and projecting at least into said necklike opening comprising the steps of injecting a plurality of gas currents of substantially equal velocity and size in substantially radial directions from the outside perimeter toward the vertical axis of said burner chamber against said guide element, whereby said gas currents are combined into a single substantially tubular gas current which is diverted by said guide element upwardly into and through said reaction chamber and then out of the upper end thereof; intermittently charging said reaction chamber with a predetermined amount of said granular material in the form of separate particles so as to pass said particles from above into the ascending tubular gas current; maintaining a repeated circulating movement of said particles in said reaction chamber in which during the ascending part of said movement said particles are carried upwardly by said gas current to a point near the upper end of said chamber, whereupon said particles are caused to separate from the further ascending gas current and to fall by gravity outside of said gas current along the r wall of said reaction chamber toward said necklike opening where said particles are again picked up and carried upwardly by said gas current; and then intermittently removing the expanded particles from said reaction chamber.

3. A method of expanding an expansible granular material in a hot gas current in a vertical reaction chamber having a burner chamber underneath and substantially coaxial thereto and communicating therewith through a central necklike opening comprising the steps of injecting a plurality of gas currents of substantially equal velocity and size in substantially radial directions from the outside perimeter toward the vertical axis of said burner chamber, and then combining said gas currents and deflecting the same as one substantially symmetrical beamlike gas current upwardly into and through said reaction chamber and then out of the upper end thereof; intermittently charging said reaction chamber with a predetermined amount of said granular material in the form of separate particles so as to pass said particles from above into the ascending gas current; maintaining a repeated circulating movement of said particles in said reaction chamber in which during the ascending part of said movement, said particles are carried upwardly to a certain culmination level within said reaction chamber where the buoyancy of said gas current no longer exceeds the gravity of said particles, whereupon said particles separate of their own accord from the further ascending gas current and fall downwardly outside of said gas current along the wall of said reaction chamber toward said neckline opening where said partticles are again picked up and carried upwardly by said gas current; and then intermittently removing the expanded particles from said reaction chamber.

4. A method of expanding an expansible granular material in a hot gas current in a vertical reaction chamber having a burner chamber underneath and substantially coaxial thereto and communicating therewith through a central necklike opening and further having a vertical guide element within said burner chamber coaxially with said reaction chamber and projecting at least into said necklike opening and substantially conically diverging toward its upper end comprising the steps of injecting a plurality of gas currents of substantially equal velocity and size in substantially radial directions from the outside perimeter toward the vertical axis of said burner chamber against said conical guide element, whereby said gas currents are combined into a single substantially tubular gas current which is diverted by said guide element upwardly into the reaction chamber and conically outwardly toward the wall of said chamber and then through said chamber and out of the upper end thereof; intermittently charging said reaction chamber with a certain amount of said granular material in the form of separate particles so as to pass said particles from above into the ascending conical gas current; maintaining a repeated circulating movement of said particles in said reaction chamber in which during the ascending part of said movement said particles are carried upwardly by said gas current and at an acute angle toward and upwardly along the wall of said reaction chamber to a certain culmination level Where the buoyancy of said gas current no longer exceeds the gravity of said particles, whereupon said particles separate of their own accord from the further ascending gas current and fall downwardly along said wall toward said necklike opening where said particles are again picked up and carried upwardly by said gas current; and then intermittently removing the expanded particles from said reaction chamber.

5. A method as defined in claim 3, in which said expanded particles are removed from said reaction chamber by at least partly lowering said guide element through an axial discharge port in the bottom of said burner chamber and by thereby opening said port so that said particles will drop from said reaction chamber through said burner chamber and out of said port.

6. A method as defined in claim 1, comprising the fur ther step of positively deflecting said particles at the end of their descending movement from the wall of said reaction chamber toward said vertical axis thereof and upwardly in a substantially conically converging direction back into the ascending gas current.

7. A method as defined in claim 1, comprising the further step of injecting a plurality of additional gas currents in substantially radial directions into said reaction chamber near the lower end thereof so as to deflect said particles at the end of their descending movement from the wall of said reaction chamber toward said vertical axis thereof and upwardly back into the ascending gas current 8. A method as defined in claim 1, comprising the further step of injecting an additional gas current uniformly from the outside in substantially all radial directions into said reaction chamber near the lower end thereof so as to deflect said particles at the end of their descending movement from the wall of said reaction chamber toward said vertical axis thereof and upwardly back into the ascending gas current 9. An apparatus for expanding an expansible granular material in a hot gas current comprising a vertical reaction chamber; a burner chamber underneath said reaction chamber and having an upper neck part of a smaller inner diameter than said chambers and connecting said chambers, the common vertical axis of said reaction chamber and said neck portion extending into said burner chamber; a plurality of nozzles in said burner chamber equally spaced from each other and from said vertical axis and extending in radial directions for directing a plurality of hot gas currents toward said axis so as to combine said currents to form a single central beamlike gas current; means for directing said current centrally through said neck part into said reaction chamber; and means for feeding said granular material in the form of separate particles into said reaction chamber and into the ascending gas current for producing a circulating movement of said particles in an upwardly and downwardly direction in said reaction chamber.

10. An apparatus as defined in claim 9, further comprising means for supplying a fuel gas to said nozzles, said nozzles forming burners for producing a plurality of flames directed toward said axis; and means for passing secondary air into said burner chamber in an angular direction to and intersecting with the axis of each of said flames for reducing the length of said flames.

11. An apparatus as defined in claim 9, in which said burner chamber has top, side and bottom walls, at least said top and side Walls each having an inner and outer wall spaced from each other so as to form an intermediate chamberlike channel; means for passing air into said channel for cooling said walls; said inner walls having first and second apertures therein, said first apertures adapted to pass primary air from said channel to each of said burners, and said second apertures adapted to pass secondary air into said burner chamber in an angular direction to and intersecting with the axis of each of said flames for reducing the length of said flames.

12. An apparatus as defined in claim 9, in which said neck part intermediate said chambers also has inner and outer walls so as to form an intermediate chamberlike channel for cooling said walls; said channel communicating with said channel between said top and side walls.

13. An apparatus as defined in claim 11, in which said bottom wall of said burner chamber comprises refractory material.

14. An apparatus as defined in claim 9, in which said burner chamber has an annular shape and contains a guide element centrally mounted on the bottom of said burner chamber and coaxial with and extending into said reaction chamber; said guide element adapted to intercept said gas currents, combined them into a single tubular current, and then deflect said current upwardly into said reaction chamber in a direction symmetrical to the side wall thereof.

15. An apparatus as defined in claim 14, in which the lower part of said guide element forms a lateral concave guide surface adapted to intercept and combine said gas currents and to deflect the same upwardly as a single tubular current.

16. An apparatus as defined in claim 15, in which said reaction chamber has a lower part with an inner wall of a conical downwardly converging shape connected at its lower end to said neck part; the extension of the generatrix of said inner wall intersecting with said concave guide surface of said guide element.

17. An apparatus as defined in claim 15, in which the upper part of said guide element has a vertical cylindrical shape so as to form a cylindrical tubular gas current in said reaction chamber; said concave lower guide surface merging smoothly with said upper part.

'18. An apparatus as defined in claim 15, in which the upper part of said guide element diverges substantially conically from said lower concave guide surface into said reaction chamber so as to form a conical tubular gas current in said reaction chamber.

19. An apparatus as defined in claim 14, in which said guide element is hollow and consists of a highly refractory material; and means for conducting air into said guide element for cooling same.

20. An apparatus as defined in claim 15, in which said guide element is hollow and has a plurality of apertures therein underneath said concave guide surface; and means for conducting air under pressure into said guide element for cooling the same and for passing through said apertures into said gas currents in a direction opposite to the part thereof coming from said nozzles for blowing any particles which have dropped so far downwardly back into said gas currents so as to be picked up and carried by them again upwardly into said reaction chamber.

21. An apparatus as defined in claim 20, in which the axis of each of said apertures extends at an upwardly oblique angle so as to blow said air upwardly into said neck portion and the tubular air current ascending therein.

22. An apparatus as defined in claim 21, further comprising baffie means in the form of a bafile surface on said guide element directly underneath said apertures for preventing any particles from passing downwardly past said apertures to the bottom of said burner chamber.

23. An apparatus as defined in claim 22, in which said baffie surface extends substantially parallel to the oblique axis of each of said apertures.

24. An apparatus as defined in claim 14, in which the bottom of said burner chamber has a discharge port therein coaxially to said reaction chamber for removing the expanded particles from said reaction chamber through said burner chamber; and a closure member adapted to be raised and lowered for closing and opening said discharge port, said guide element being mounted on said closure member so as to be raised and lowered therewith.

25. An apparatus as defined in claim 9, in which said reaction chamber has a lower part with an inner wall of a conical downwardly converging shape connected at its lower end to said neck part and an annular surface at the lower end of said conical lower part projecting in the direction toward said tubular gas current for passing the particles at the lower end of their descending movement back into the ascending gas current by employing the gravitational force of said particles.

26. An apparatus as defined in claim 25, in which said annular surface has a substantially trough-shaped cross section adapted under the action of said gravitational force to pass said particles in an upwardly obliquely inclined direction into said ascending gas current.

27. An apparatus as defined in claim 26, in which the wall of said lower end of said conical lower part of said reaction chamber has at least one channel therein extending from the outside through said wall in a direction substantially tangential to said trough-shaped surface for blowing a gas along said surface toward the inside of said reaction chamber for accelerating the movement of said particles oif said surface into said ascending gas current.

28. An apparatus as defined in claim 9, in which said reaction chamber has such a height that the top wall of said chamber and a flue outlet therein are disposed above the culmination level of said particles in said chamber where the buoyancy of the ascending gas current no longer exceeds the gravity of said particles, and said particles separate of their own accord from the further ascending gas current and fall outwardly thereof and along the side wall of said reaction chamber toward said neck part of said burner chamber and are then picked up again and carried upwardly by said ascending gas current for the next circulating movement of said particles.

References Cited UNITED STATES PATENTS 2,932,498 4/1960 Metcalfe et a1. 263-21 3,201,099 8/1965 Carpenter 263-21 JOHN J. CAMBY, Primary Examiner.

US. Cl. X.R. 252-378 

